T&T: Alternator-Tachometer Problem

[Stephen Offutt]

I would like a little advice on where to start with this problem.  My port
Perkins 6.354-4 Engine had started fine and I ran the throttle up to about
1300 rpm to kick off the alternator input to the tachometer.  This is normal
behavior for these 65amp alternators; I think they are called 'two wire
alternators'.

The tachometer ran up as normal.  It tracked fine with the throttle run-up
to 2000 rpm.  I then started the starboard engine in same sequence; with the
same normal response.  

After 7-10 minutes, I noticed that the port tachometer had dropped to zero.
The port engine was still running fine.  Running the engine up to about
2000rpm did not restart the tachometer.  I killed the engine and went
through normal start procedures twice with no effect on the tachometer
reading.  It stayed stuck on zero.

Of course the first question would be: did the port battery charging meter
run-up to the normal its normal level.  It did on the first start - I always
check that.  I did not think to check that on the two subsequent re-starts
and run-ups - woops :)- I just thought of that.

That is the problem.  I would greatly appreciate any troubleshooting advice
and guesses at the problem.  The good news is that the port engine
alternator is inboard and easily accessed, unlike the starboard outboard
alternator.

Thanks for any help,

Stephen V. Offutt
stephen at ourdutchmaster.com